An important goal of gene therapy is to deliver genes so that they express in a pattern that mimics the expression of an endogenous cellular gene. Gene delivery vectors developed for this purpose will need to carry transcriptional and genomic regulatory elements. This application focuses on developing lentiviral vectors that can express genes in a regulated manner in CD4+ T cells by using the transcriptional control elements of the CD4 and CD40 ligand genes. Lentiviral vectors will be constructed, packaged, and evaluated that carry different combinations of transcriptional control elements to determine the components necessary to regulate expression in CD4+ T cells, eGFP, which can be measured quantitatively by flow cytometry and used to isolate vector-expressing cells by FACS sorting, will be used as the reporter gene. Gene transfer and expression from these vectors will be assessed in cell lines, primary human T cells, and blood cells derived from trans-planted murine hematopoietic stem cells. Scientifically, these studies will determine the utility of lentiviral vectors for regulated gene expression in CD4+ T cells and as reporter genes to identify cells capable of expressing from the CD4 or CD40 ligand promoter under different physiologic conditions. More importantly, these studies will provide the background necessary for developing vectors capable of expressing therapeutic genes in a highly regulated manner in CD4+ T cells, which would have applications in treating diseases (HIV infection, genetic deficiencies) or in vaccine strategies. [unreadable] [unreadable]